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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Polarons are probes of the dynamic nanoscale environments found in electrochemically doped π-conjugated polymers

Charge carriers (i.e., polarons) in electrochemically doped organic (semi)conductors are proposed to be regulated by several physicochemical features, including the chemical compositions and structures of the π-conjugated frameworks of the semiconductor building blocks, the chemistry of the electrolyte (considering both the salt and solvent), multiscale and time-dependent morphology variations across the material as a function of electrochemical processes, and assorted permutations of these and other factors. To address these hypotheses, we investigate the energetic, optoelectronic, chemical, and local structural properties of negative polarons (radical anions) as a function of electrochemical doping in the donor–acceptor, π-conjugated redox copolymer P(NDI2OD-T2), also referred to as N2200. A critical finding is that there is not just “one type” of polaron in electrochemically doped P(NDI2OD-T2). Rather, an ensemble of polarons exists, with the polarons having optoelectronic signatures that are defined by their nanoscale environments. Importantly, the polaron optical signatures serve as local probes for how the operando electrochemical environments are dynamically working in concert to facilitate charge transport. Collectively, the distinctive and extensive integration of theory and measurement science presented here establishes a baseline for the roles that semiconductor and electrolyte chemistries and dynamic structural features have on polarons in electrochemically doped organic semiconductors and how these factors influence the energetics and rates of polaron transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Ellipsometric study of metal-organic chemically vapor deposited III-V semiconductor structures

An ellipsometric study of MOCVD-grown layers of AlGaAs and InGaAs in thick films and strained layer complex structures is presented. It is concluded that the ternary composition of thick nonstrained layers can be accurately determined to within experimental errors using numerical algorithms. In the case of complex structures, thickness of all layers and the alloy composition of nonstrained layers can be determined simultaneously, provided that the correlations between parameters is no higher than 0.9.

Alterovitz, Samuel A.↗
DOE OSTI2025

Optical Activity of Chiral Excitons

Recent activity in the area of chiroptical phenomena has been focused on the connection between structural asymmetry, electron spin configuration and light/matter interactions in chiral semiconductors. In these systems, spin‐splitting phenomena emerge due to inversion symmetry breaking and the presence of extended electronic states, yet the connection to chiroptical phenomena is lacking. Here, in this study, we develop an analytical effective mass model of chiral excitons, parameterized by density functional theory. The model accounts for parity mixing of the band edge Bloch functions resulting from polar distortions, resulting in allowed magnetic dipole transitions. Through the study of a prototypical chiral 2D hybrid perovskite semiconductor, we show that circular dichroism of the chiral exciton and its interband continuum emerges from spin‐splitting via cross‐coupling of Rashba‐like and chiral/helical spin‐texture components. To demonstrate the generality of our approach, and as a counterpoint, we apply our model to describe chiroptical properties of three‐dimensionally confined excitons in perovskite nanocrystals that occur without chiral lattice distortions.

14 SOLAR ENERGY↗
DOE OSTI2020

Semiclassical model for calculating exciton and polaron pair energetics at interfaces

Exciton and polaron pair dissociation is a key functional aspect of photovoltaic devices. To improve upon the current state of interfacial transport models, we augment the existing classical models of dielectric interfaces by incorporating results from ab initio calculations, allowing us to calculate exciton and polaron binding energies more accurately. We demonstrate the predictive capabilities of this new model using two interfaces: (i) the boron subphthalocyanine chloride (SubPc) and C60 interface, which is an archetype for many organic photovoltaic devices; and (ii) pentacene and silicon (1 0 0), which represents a hybrid between organic and inorganic semiconductors. Overall, our calculations predict that the insertion of molecular dipoles at interfaces can be used for improving polaron pair dissociation and that sharp transitions in dielectric permittivity can have a stronger effect on the polaron pair dissociation than even the electron-hole Coulomb interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Measuring Vibronic Coupling and Ultrafast Charge Delocalization on Nanocrystal Surfaces Using Ligand-Specific Vibrational Probes

The primary goal of this proposal was to measure and quantify how vibronic ligand-exciton interactions at the inorganic-organic interface of semiconductor nanocrystals (NCs) govern femtosecond non-radiative relaxation and charge delocalization mechanisms as a function of nanocrystal and ligand structures – including NC size, shape, and ligand identity. Molecular-scale chemical and physical properties and interactions of surface ligands dictate nanocrystal exciton dynamics on the femto-to-microsecond timescales. Improvements in synthesis, experimental, and theoretical characterizations have enhanced our understanding of NC photophysics. However, quantitative descriptions of complex ligand-exciton interactions at the NC surface have remained elusive, which limits elucidation of relaxation mechanisms that determine overall carrier transfer dynamics at the exciton-ligand interface. Thus, the central motivation for this proposal was to fill a significant knowledge gap for judicious selection of ligand-functionalized nanocrystals for targeted isolation and capture of charge carriers to drive selective organic photocatalytic transformations in NC photocatalysts and NC-assembled photonic materials. Our unique two-pronged experimental approach combining nanocrystal synthesis and ligand-specific nonlinear spectroscopy has resulted in (i) four peer-reviewed publications; (ii) 12+ invited and contributed posters and talks at national and international scientific meetings and seminars, (iii) two completed PhD theses, (iv) training of two postdoctoral researchers, three PhD students, and two undergraduate students, and (v) two manuscripts under preparation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Vibronic Excitons and Conical Intersections in Semiconductor Quantum Dots

Surface defects and organic surface-capping ligands affect the photoluminescence properties of semiconductor quantum dots (QDs) by altering the rates of competing nonradiative relaxation processes. In this study, broadband two-dimensional electronic spectroscopy reveals that absorption of light by QDs prepares vibronic excitons, excited states derived from quantum coherent mixing of the core electronic and ligand vibrational states. Rapidly damped coherent wavepacket motions of the ligands are observed during hot-carrier cooling, with vibronic coherence transferred to the photoluminescent state. Furthermore, these findings suggest a many-electron, molecular theory for the electronic structure of QDs, which is supported by calculations of the structures of conical intersections between the exciton potential surfaces of a small ammonia-passivated model CdSe nanoparticle.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Phase transitions of β-ZnTe(en) 0.5 under hydrostatic pressure

Organic–inorganic hybrid semiconductors have enhanced and distinctive material properties. β-ZnTe(en) 0.5 , which consists of alternating layers of two-monolayer-thick zinc telluride (ZnTe) and ethylenediamine (en), exhibits high crystallinity, stability, and tunable optical properties. Using x-ray diffraction (XRD) and Fourier transform infrared spectroscopy, this study investigated the structural response of β-ZnTe(en) 0.5 to applied hydrostatic pressure. Pressure-induced phase transitions were observed at 2.1 and 3.3 GPa. Shifts in the XRD peaks indicate substantial anisotropy in the pressure response, with the layer stacking direction ( b axis) exhibiting high compressibility. The a and b lattice parameters showed −0.55% strain/GPa and −2.26% strain/GPa, respectively, contradicting theoretical calculations that predicted a more isotropic response. IR spectroscopy revealed abrupt changes in NH 2 and CH 2 vibrational modes corresponding to the phase transitions.

Chemical compounds↗
DOE OSTI2024

WoRDMAp Outbrief: Workshop on Radiation Detection Materials [Slides]

Project Goal: Identify pathway to reliably grow and fabricate high-performance radiation detectors for use in a variety of nonproliferation applications. 1. Create 3 working groups (semiconductors, inorganic and organic scintillators) that bring together international R&D subject-matter experts (national laboratories, industry, and academia), end users, and mission stakeholders 2. Reach expert consensus views regarding current materials related technology gaps and define prioritized R&D directions required to resolve these gaps 3. Envisage the future state of next-generation radiation detection materials and quantify the benefits to nuclear security applications 4. Provide a comprehensive expert report to DNN R&D program office to serve as roadmap with recommendations for future high-impact office investment in radiation-detection materials development

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Control of light, spin and charge with chiral metal halide semiconductors

We report the relationship between the structural asymmetry and optoelectronic properties of functional materials is an active area of research. The movement of charges through an oriented chiral medium depends on the spin configuration of the charges, and such systems can be used to control spin populations without magnetic components - termed the chiral-induced spin selectivity (CISS) effect. CISS has mainly been studied in chiral organic molecules and their assemblies. Semiconductors are non-magnetic extended systems that allow for the control of charge transport, as well as the absorption and emission of light. Therefore, introducing chirality into semiconductors would enable control over charge, spin and light without magnetic components. Chiral metal halide semiconductors (MHSs) are hybrid organic-inorganic materials that combine the properties of small chiral organic molecules with those of extended inorganic semiconductors. Reports of CISS in chiral MHSs have resulted in breakthroughs in our understanding of CISS and in the realization of spin-dependent optoelectronic properties. This Review examines the fundamentals and applications of CISS in chiral MHSs. The structural diversity and key structure-property relationships, such as chiral transfer from the organic to the inorganic components, are summarized. With a focus on the underlying chemistry and physics, the control of spin, light and charge in these semiconductors is explored.

14 SOLAR ENERGY↗
DOE OSTI2020

Fast Organic Vapor Phase Deposition of Thin Films in Light-Emitting Diodes

Fast deposition of thin films is essential for achieving low-cost, high throughput phosphorescent organic light emitting diode (PHOLED) production. In this work, we demonstrate rapid and uniform growth of semiconductor thin films by organic vapor phase deposition (OVPD). A green PHOLED comprising an emission layer (EML) grown at 50 Å/s with bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (Ir(ppy)2(acac)) doped into 4,4 bis(N-carbazolyl)-1,1zolylld (CBP) exhibits a maximum external quantum efficiency of 20 ± 1%. The morphology, charge transport properties, and radiative efficiency under optical and electrical excitation of the PHOLED EML are investigated as functions of the deposition rate via both experimental and theoretical approaches. The EML shows no evidence for gas phase nucleation of the organic molecules at deposition rates as high as 50 Å/s. However, the roll-off in quantum efficiency at high current progressively increases with deposition rate due to enhanced triplet-polaron annihilation. The roll-off results from accumulation of stress within the PHOLED EML that generates a high density of defect states. Here, the defects, in turn, act as recombination sites for triplets and hole polarons, leading to enhanced triplet-polaron annihilation at high current. We introduce a void nucleation model to describe the film morphology evolution that is observed using electron microscopy.

42 ENGINEERING↗
NASA NTRS1994

Growing Organic Crystals By The Czochralski Method

Apparatus grows high-quality single crystals of organic compounds by Czochralski method. In Czochralski process, growing crystal lifted from middle of molten material without touching walls. Because of low melting temperatures of organic crystals, glass vessels usable. Traditional method for inorganic semiconductors adapted to optically nonlinear organic materials.

Shields, Angela↗
DOE OSTI2021

From n- to p-type material: Effect of Metal Ion on Charge Transport in Metal-Organic Materials

An intriguing new class of two-dimensional (2D) materials based on metal–organic frameworks (MOFs) has recently been developed that displays electrical conductivity, a rarity among these nanoporous materials. The emergence of conducting MOFs raises questions about their fundamental electronic properties, but few studies exist in this regard. Here, we present an integrated theory and experimental investigation to probe the effects of metal substitution on the charge transport properties of M-HITP, where M = Ni or Pt and HITP = 2,3,6,7,10,11-hexaiminotriphenylene. The results show that the identity of the M-HITP majority charge carrier can be changed without intentional introduction of electronically active dopants. We observe that the selection of the metal ion substantially affects charge transport. Using the known structure, Ni-HITP, we synthesized a new amorphous material, a-Pt-HITP, which although amorphous is nevertheless found to be porous upon desolvation. Importantly, this new material exhibits p-type charge transport behavior, unlike Ni-HITP, which displays n-type charge transport. These results demonstrate that both p- and n-type materials can be achieved within the same MOF topology through appropriate choice of the metal ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

In-Situ Ligand-Induced Chirality Transfer in Emissive CdSe Nanoplatelets

Terminating semiconductor nanocrystals with chiral organic ligands can induce chiroptical properties that combine the chiral character of the ligands with the strong and tunable optical properties of the nanocrystal. However, the synthesis of such chiral-modified nanocrystals is currently limited by solvent incompatibility between polar chiral ligands and nonpolar traditional ligands, as well as by ligand dissolution behavior that ultimately compromises nanocrystal quality and the degree to which chiroptical properties can be manipulated. In this work, we demonstrate a single-step synthesis of chiral cadmium selenide (CdSe) nanoplatelets (NPLs) that eliminates the need for postsynthetic ligand exchange in aqueous solvents, resulting in highly emissive chiral CdSe NPLs. By directly incorporating chiral aminodecanoic acid ligands during synthesis, we achieve in situ ligand binding and chirality transfer to CdSe NPLs. This approach produces CdSe NPLs with high photoluminescence quantum efficiencies of 50% and circular dichroism dissymmetry factors (gCD) on the order of 10 –4 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

DRiFT - Release 2.1.0: Organic Scintillators and Gas Detectors

DRiFT (a Detector Response Function Toolkit) is LANL-developed software that post-processes output from the extensively validated radiation transport code, MCNP, and generates realistic nuclear instrumentation response. DRiFT is designed to be flexible, enabling users to specify detector type and many experimental settings, as well as accommodating the addition of their own desired features. The focus of this release is on organic scintillator, gas detector, and associated capabilities, while semiconductor features are still under development. Organic scintillators are widely used in the areas of nuclear safeguards and nuclear non-proliferation efforts. DRiFT has several diagnostic and detector physics features relevant to detailed scintillator simulations including: tracking source particle information, scintillation light production, the effects of PMT quantum efficiency and gain, and digitizer settings. Users can select responses from many scintillator and PMT types supported natively by DRiFT, or add their own by following the instructions in this document. DRiFT also has several diagnostic and detector physics features relevant to neutron gas detector simulations including: gas detector wall effects, inactive areas at the end of detector tubes, and effects of a preamplifier. We acknowledge that DRiFT is under active development, bug reports and general questions and comments should be directed to Madison Andrews, madison@lanl.gov. This manual is divided into four parts: I) An overview of DRiFT, including how to obtain and install the executable, II) A description of the detector physics related to scintillators available, III) a description of more general DRiFT features the user may find useful, and IV) a description of the test suite and examples made available with the code release.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Role of Polycyclic Aromatic Alkylammonium Cations in Tuning the Electronic Properties and Band Alignment of Two-Dimensional Hybrid Perovskite Semiconductors

Two-dimensional hybrid organic–inorganic perovskites (HOIPs) have recently drawn intense attention as potential photovoltaic materials. However, n = 1 two-dimensional (2D) HOIPs face the challenge of low conductivity between the inorganic layers, leading to unsatisfactory device performance. Interestingly, 2D HOIPs employing π-conjugated molecules as organic moieties show energy and charge transfers between organic and inorganic layers, indicating potentially efficient carrier transport for photovoltaic applications. Nevertheless, the development of 2D HOIP-based solar cells especially utilizing polycyclic aromatic alkylammonium as cations is in its infancy. Herein, we investigated the electronic structure and band alignment of a series of n = 1 2D Ruddlesden–Popper (RP) phase HOIPs containing different polycyclic aromatic groups and alkyl chains, based on density functional theory calculations. We find that the polycyclic aromatic group plays an important role in controlling the functionality of 2D HOIPs by directly modifying band-edge states, and the band alignment at the organic–inorganic interface can be designed to promote either exciton trapping or dissociation for light-emitting or photovoltaic applications, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Photoredox Organic Synthesis Employing Heterogeneous Photocatalysts with Emphasis on Halide Perovskite

Abstract Lately, heterogeneous semiconductor materials have been explored as an emerging type of efficient photocatalyst for photoredox organic synthesis. Among these semiconductors, lead halide perovskite materials demonstrate unique properties towards excellent charge separation and charge transfer, extremely long charge carrier migration, high efficiency in visible light absorption, and long excited states lifetimes, etc., as proved in ground‐breaking solar cell applications, garnering necessary merits for an efficient catalytic system for photoredox organic reactions. Here, the latest progress in heterogeneous semiconductor materials towards this endeavor is examined, with particular emphasis on lead halide perovskite nanocrystals (NCs) in photocatalytic organic synthesis.

Lin, Yixiong↗
DOE OSTI2023

Ratiometric vapor sensor

A ratiometric vapor sensor is described that includes a first sensor and a second sensor. The first sensor includes a first semiconductor component comprising a vapor-sensitive semiconducting organic compound, while the second sensor includes a second semiconductor component comprising a modified vapor-sensitive semiconducting organic compound including a modifying organic group. The ratiometric vapor sensor can be used to detect the presence of a vapor such as nitrogen dioxide, and determine the concentration of the vapor by comparing the outputs of electrodes connected to the first and second sensor.

47 OTHER INSTRUMENTATION↗
NASA NTRS1990

Photoreflectance for in-situ characterization of MOCVD growth of semiconductors under micro-gravity conditions

A contactless electromodulation technique of photoreflectance (PR) was developed for in-situ monitoring of metal-organic chemical vapor deposition (MOCVD) semiconductor growth for micro-gravity applications. PR can be employed in a real MOCVD reactor including rotating substrate (approximately 500 rev/min) in flowing gases and through a diffuser plate. Measurements on GaAs and Ga(0.82)Al(0.18)As were made up to 690 C. The direct band gaps of In(x)Ga(1-x)As (x = 0.07 and 0.16) were evaluated up to 600 C. In order to address the question of real time measurement, the spectra of the direct gap of GaAs at 650 C was obtained in 30 seconds and 15 seconds seems feasible.

Pollak, Fred H.↗